The general objective of this proposal is to elucidate the mechanisms by which the interaction of actin and myosin underlying contraction of vascular smooth muscle is regulated in normal and hypertensive blood vessels. This proposal is based upon the hypothesis that the degree of phosphorylation of myosin directly controls force development in vascular smooth muscle. In order to investigate this hypothesis, the following studies are proposed to 1) investigation of the factors which control the degree of phosphorylation of myosin light chains. Strips of arterial smooth muscle stretched to Lmax will be activated by potassium depolarization and frozen in liquid nitrogen. The myosin light chains will be separated and the degree of phosphorylation determined. The time course and magnitude of phosphorylation and isometric force development will be compared at different degrees of activation, i.e., (K ion)o. Detailed studies will be made on the control of actin-activated myosin ATPase activity, and of the degree of myosin phosphorylation by kinase and phosphatase enzyme systems.